Of the various types of thread rolling machines in commercial use, several use one or more dies of cylindrical shape, commonly called "circular dies." Planetary thread rollers use a single circular die that rotates continuously about a fixed axis, plus one or more stationary, concave shaped die segments located adjacent the periphery of the rotating die. There are two other basic types of thread rolling machines using cylindrical dies: one having two dies mounted diametrically opposite each other, and the other equipped with three equally spaced, parallel axis, cylindrical dies. In all these machines the circular dies, being perishable tooling, must be mounted and removed from the machines at intervals. The problems involved are common to all the above-mentioned classes of machines.
This invention is concerned with the means provided for mounting a circular die on the machine spindle. Thread rollers manufactured heretofore commonly provided a simple clearance fit with a driving key between the die and the spindle. Even though close manufacturing tolerances are observed, the cyclical nature of the load in thread rolling inevitably causes fretting corrosion between die and spindle. It is a serious problem and results in hours spent (literally) in the frustrating job of removing the die from its spindle. Fretting corrosion also produces gradual destruction of both surfaces as is well known.